The present invention relates to a noise monitoring system, and in particular to a noise monitoring system and method for continuously and accurately monitoring an individual""s noise exposure during periods when an individual""s hearing protective device is occluding the ear, and when such device is being worn in an off-the-ear position.
The U.S. Department of Labor Occupational Noise Exposure Standard (29 C.F.R. xc2xa7 1910.95) specifies that noise dosimetry may be used to measure noise exposure on individuals in the workplace. The standard specifies that individuals exposed to greater than 85 dBA Time-Weighted Average (xe2x80x9cTWAxe2x80x9d) must be included in a comprehensive hearing conservation program (xe2x80x9cHCPxe2x80x9d). The allowable exposure to noise is measured in terms of cumulative noise dose, i.e., individuals are considered to be within compliance if they are exposed to less than 90 dBA TWA (a 100% dose) over an 8 hour work day. Total noise dose during the work day is given by D=100 (C1/T1+C2/T2 + . . . Cn/Tn), where D is the percentage noise dose, C is the total length of the specific exposure, in hours, and T is the reference duration corresponding to the measured sound level (see 29 C.F.R. xc2xa7 1910.95, Table G-16A, 1999). A TWA of the A-weighted sound level may be calculated from the dose measurement by means of the formula: TWA=16.61 log10 (D/100)+90. This provides a mechanism for accumulating exposures of varying levels and durations where an xe2x80x9cexchange ratexe2x80x9d of 5 dB per doubling of time is used to evaluate exposure levels. For example, an exposure of 90 dBA for 4 hours is considered equivalent to either 1) an exposure of 85 dBA for 8 hours, or 2) an exposure of 95 dBA for 2 hours. Noise dosimeters are employed to measure cumulative noise dose by applying the xe2x80x9cexchange ratexe2x80x9d to the level and duration of exposure.
Noise dosimetry is commonly used in industry, and the measurements are usually intended to indicate the cumulative exposure to noise over the course of a full work shift. In addition to determining which employees should be included in the HCP, these measurements are commonly used to determine hearing protector requirements, and to determine noise control requirements. The information gathered by noise dosimeters is typically used by industrial personnel only, i.e., this information is not intended for interpretation by the worker. In many instances, the readouts of dosimeters are sealed shut so that the wearer has no visible indication of current exposure or dose.
Currently existing hearing protective devices (xe2x80x9cHPDxe2x80x9d) such as ear muffs, ear plugs, and semi-aural devices, provide widely variable attenuation in the workplace and the laboratory ratings of a HPD""s performance may grossly overestimate the protection afforded some individuals. There are several methods of measuring the effectiveness of hearing protectors on the end-users, but these methods are point measurements, i.e., measurements made to determine the attenuation provided by the HPDs after one fitting of the device. Point measurement apparatus and methods are described in Epley (U.S. Pat. Nos. 4,060,701; 4,020,298); Padilla (U.S. Pat. No. 3,968,334); and Seidemann (U.S. Pat. No. 5,757,930). A major disadvantage of evaluating hearing protector effectiveness by point measurement is that no insight is provided into the actual protection afforded the HPD wearer at any time, or period of time, other than during the measurement session.
Continuous monitoring of personal noise exposure with conventional hardware is both cumbersome and prohibitively expensive. Conventional noise dosimeters are not intended for use on every employee during every work shift, and are far too expensive to be used on a daily basis on every employee.
Conventional noise dose measurements are intended to be performed with the dosimeter microphone mounted on the shoulder of the employee. This microphone placement technique accurately measures noise dose, but does not take into account the noise reduction provided by the HPD. While it is possible to mount the conventional dosimeter microphone inside a muff-type HPD to measure noise dose while wearing muffs, the hardware configuration is awkward, prohibitively expensive, and not suitable for everyday use.
Evans (U.S. Pat. No. 4,307,385) describes a noise monitoring device, but it is not designed for accurate measurements when not being worn by the user in an over the ear position. This is a major disadvantage of the Evans system since the overall accuracy of measurements will be compromised during periods when the HPD is not donned. The Evans system measures noise exposure when the HPD is worn, but the system does not measure the overall noise exposure to the hearing protector wearer over the course of an average workday, which includes periods when the HPD is not donned.
Damage-risk criteria for predicting the incidence of noise-induced hearing loss (xe2x80x9cNIHLxe2x80x9d) among populations of workers as a function of workplace noise levels and exposures are the basis of all current occupational noise regulations in the United States. The development of these fundamental damage-risk criteria is based primarily on an assessment of workplace noise levels as measured in a diffuse field at the worker""s center-of-head (xe2x80x9cCOHxe2x80x9d) location, but with the worker absent. Thus, it is of the utmost importance that any determination of a worker""s protected, or unprotected, noise exposure be correlated to an equivalent COH dose. For example, the popular top-of-the-shoulder microphone location utilized for conducting a personal noise dosimeter measurement of a worker""s unprotected noise exposure is simply a convenient and practical surrogate for the true COH location. Measurement of a worker""s noise dose using this substitute location provides a reasonably accurate approximation of the worker""s true COH noise exposure for most industrial acoustical conditions. However, other locations in the vicinity of the worker""s head, or in the ear, are just as suitable as surrogates, especially with the availability of miniature microphones.
Workers in the United States continue to experience an unacceptably high incidence of NIHL despite the existence of federal legislation designed to prevent such injuries. Much of the current state of hearing conservation can be attributed directly to the reliance, over the last 30 years, on limited or single-shift noise exposure data and personal hearing protection as the first, and only, line of defense against hazardous noise. Moreover, past efforts to protect workers from occupational noise have focused primarily on achieving compliance with the noise regulations, rather than prevention. While a single shift measurement of noise exposure is sufficient for compliance purposes, it fails to account for the highly variable daily noise exposures found in general industry. Numerous studies have also documented that the deficiencies associated with personal hearing protectors and their use make it virtually impossible to accurately predict, based on laboratory-derived performance data, their effectiveness in reducing workplace noise exposures. As a result of this ambiguity in both short and long-term noise exposures, many workers have remained overexposed. No strategy to prevent NIHL will ever be effective until this ambiguity in worker noise exposure is eliminated. Thus, a new solution is needed to resolve this ambiguity and facilitate the upstream prevention of NIHL.
The current invention is a system and method for reducing noise exposure and for the continuous monitoring of personal noise exposure. It involves the integration of personal noise dosimetry with a standard hearing protector in such a manner that, the worker""s actual noise exposure is accurately measured under all acceptable wearing conditions. Analytical and empirical techniques demonstrate that the surrogate primary and secondary microphone measurement locations, as defined and employed in the subject system and method, yield noise exposures that are accurate estimates of their equivalent COH noise exposures. The method and apparatus take into account all the factors contributing to exposure ambiguity, such as fit and wearing time, that otherwise limit and ultimately control the effectiveness of a traditional hearing protector. An integral part of the system and method of the present invention is continuous monitoring, which can be used to ensure that a worker is protected to a safe noise exposure level on a daily basis, as well as to document the worker""s long-term noise exposure.
Consequently, there is a need for a device that provides a means of continuously monitoring an individual""s actual noise exposure rather than simply measuring either hearing protector attenuation or unprotected individual exposure.
There has now been invented and disclosed herein, a certain new and novel system and method for reducing noise exposure, and for the continuous monitoring of personal noise exposure. The method is cost-effective and unobtrusive, therefore the noise exposure may be continuously monitored for every noise exposed employee during every work shift. The monitoring system includes at least one microphone, housed in the interior of a hearing protective device. The system is unique as it is designed to accurately measure the noise level impinging on the ear of the noise exposed employee both when the hearing protector(s) are occluding the ear, and when they are removed and worn in a secondary, off-the-ear position.
A preferred method of measuring noise exposure on the hearing protector wearer is to continuously monitor and analyze the noise impinging on the ear taking into consideration the effectiveness of the HPD. This type of monitoring requires the use of a noise dosimeter, and the dosimeter microphone must be located interior to the HPD so that the protected, as well as the unprotected noise exposure can be accurately measured.
The current invention is a continuous monitoring device (xe2x80x9cCMDxe2x80x9d). The CMD performs two functions: 1) it houses the microphone and noise dosimetry hardware; and 2) it reduces noise exposure by physically blocking noise that is incident to the ear. These personal noise exposure measurements do not rely on any laboratory estimates of HPD performance and they are intended to be performed daily, avoiding the inherent inaccuracy associated with spot sampling of noise exposure. Over a period of time the data gathered represent a complete noise exposure history during the employees"" work tenure. This type of exposure history may be valuable to the employer if the employee should seek compensation for work-related hearing loss, since the continuous measurements are performed daily, and will definitively determine if noise exposure is incurred on or off the job.
These data are available for analysis on a daily basis, so the employer can take corrective action in the event of excessive exposure to noise. Noise induced hearing loss typically occurs when hearing protectors are worn ineffectively over a long period of time, i.e., after months or years of excessive exposure. If insufficient protection by the CMD is noted and corrected by the employer after one day or a few days of excessive measurements, noise induced hearing loss will not occur.
It is unrealistic to assume that the worker will wear hearing protectors during the entire work shift. Hearing protectors, in fact, should be removed during periods of relative quiet to enhance the overall safety of the worker. An important and unique aspect of the current invention is that the CMD samples the noise impinging on the microphone both when the CMD is worn in or over the ear, and when the CMD is worn off the ear in a secondary position, thereby calculating the total noise dose incident to the wearer""s ear. Thus, the CMD is intended to be worn in either primary or secondary positions during the entire work shift: the primary position is defined as over the ears (for muff-type CMD) or inserted into the ear canals (for insert-type or semi-aural CMD) and the secondary position is defined as an acceptable manner of wearing the device without occluding the ear.
For a muff-type continuous monitoring device, one acceptable secondary position is wearing the muff headband around the neck with the muff cups extending forward under the user""s chin. For a muff-type continuous monitoring device mounted on a safety-cap, secondary positions include rotating the muff cups up, forward or backward on the safety cap. Thus, there are several defined secondary positions for this configuration. For a semi-aural device an acceptable secondary position is similar to the muff-type CMD, with the headband worn around the neck with the plugs oriented forward, under the user""s chin. For insert-type CMD wearers, an acceptable secondary position is to lay the devices on the user""s upper chest area with a connecting cord around the back of the neck. The wearing of hearing protectors in a secondary position is commonly done by noise-exposed workers and it is not an undue burden on the employee or the employer. Moreover, it is easy for the employer to visually monitor the use of the CMD, ensuring that it is worn in either the primary or an acceptable secondary position.
The current invention provides a method and system allowing accurate measurement of noise exposure over the course of the entire workday, wherein the typical workday includes periods when the CMDs are worn and periods when they are not worn. When the CMD is worn in the primary position (over the ear or inserted into the ear canal), the microphone is acoustically coupled to the entrance to the ear, measuring the noise level impinging on the ear. When the muff-type CMD is worn in a secondary position, careful consideration of microphone placement, cup construction, and filler foam type and location ensures that measurements will be indicative of the noise level impinging on the ear. When the insert-type or semi-aural CMD is worn in a secondary position, careful consideration of microphone placement, acoustic filter and coupling tube characteristics ensures that measurements will be indicative of the noise level impinging on the ear. Comparison measurements have been undertaken, and verify that the secondary position CMD microphone measurements are representative of the ambient environmental noise level impinging on the ear.
The average U.S. industrial noise exposure level is about 95 dBA, therefore only about 10-15 dBA of overall protection is usually required to reduce exposure to a safe level. If the CMD is worn effectively, i.e., during periods of high ambient noise levels, the resultant exposure to the ear will be reduced to a safe level in a great majority of typical industrial noise environments. If an excessive daily noise dose is measured by the CMD, it is likely that the device is being worn in the secondary position (off the ear) during periods of high ambient noise. In this case, the wearer must be educated and trained to wear the CMD more consistently.
An additional unique feature of the current invention is a pre-action level warning. This warning, either visual, auditory, or tactile, indicates when the CMD wearer has been exposed to a cumulative dose that is approaching the action level, which is considered to be the cumulative noise dose at which noise-induced hearing damage may occur. Exposures below the action level are, in general, considered to be safe. An administrative action should take place when the pre-action level warning is given, and may include a requirement that the employee wear the CMD in the primary position (over the ears) for the remainder of the work day or relocate out of the noisy environment. The current invention is fully programmable, allowing easy manipulation of exchange rate, criterion level, threshold level, and pre-action level warnings.
In addition, the current invention may also include an instantaneous level warning. This warning, which also may be either visual, auditory, or tactile, indicates when the CMD wearer is currently being exposed to a potentially hazardous noise level. This indicates that either 1) the CMDs should be donned to reduce the exposure level to the ear; 2) the CMDs are not donned in an effective manner, and should be adjusted to further reduce noise exposure to a safe level; or 3) if the CMDs are donned correctly, that the noise exposure level is high enough that the particular type of CMD being used is not sufficient for the level of noise to which the wearer is being exposed. In this latter case, an alternative CMD, or double-protection, i.e. muffs and plugs, should be considered.
A visual alarm may be in the form of a warning light positioned on the HPD or other dosimeter hardware such that it is noticeable to a wearer of the CMD when a pre-action level warning is triggered. Similarly, an audible alarm may be a buzzer or other tone which alerts the CMD wearer to the approaching noise over-exposure. Either type of warning indicator is effective, however, visual alarms may be limited because of the difficulty for a CMD wearer to see a visual alarm attached to an earmuff or other hardware. Audible alarms also have the disadvantage in that they must be louder than the ambient noise in order to be heard.
As an alternative, a tactile warning indicator which includes a vibrator circuit responsive to a high noise condition, functions as a pre-action level warning indicator without the above-mentioned limitations. In a preferred embodiment, the vibrator circuit comprises a pager-motor that vibrates for two seconds when a preset noise level or dose level is exceeded as discussed more fully herein. These vibrations may be repeated at various intervals to ensure that the warning is effectively delivered to the CMD wearer. The pager-motor may be mounted to the circuit board in a muff-type CMD or to other dosimeter hardware in the case of insert-type or semi-aural CMDs.
Another unique aspect of the invention is a wireless readout of cumulative noise dose, duration of measurement, percent of allowable noise dose, calibration check and unit serial number. This aspect of the invention provides a means for a simple and hands-free method for every employee to record the measurements on an everyday basis. In one embodiment of the wireless readout system, an infrared transmitter is mounted on the exterior of the muff cup, and the receiver of the infrared signal is attached to a PC data port. The users will then pass their CMD near the infrared receiver at the end of the work shift, and a software program resident on the PC will read the cumulate noise dose, duration of measurement, and related information via the infrared receiver hardware.
Other important objects, features, and advantages of the invention will be apparent to the reader from the foregoing and the appended claims and as the ensuing detailed description and discussion of the invention is read in conjunction with the accompanying drawings.